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Colloidal stability of capped silver nanoparticles in natural organic matter-containing electrolyte solutions

Abstract:

Due to their increased production and commercial applications, capped silver nanoparticles (AgNPs) have inevitably found their way into aquatic ecosystems. The mobility (fate/transport), bioavailability, reactivity, and toxicity of capped AgNPs are highly influenced by their colloidal stability. This study investigated the aggregation kinetics and interfacial interactions of tannic acid (TA)-coated or silica-coated AgNPs in natural organic matter (NOM)-containing electrolyte solutions by time-resolved dynamic light scattering and atomic force microscopy. Three well-characterized NOM fractions of different characteristics were selected. In Na+-solutions, the polymeric TA induced more stability to AgNPs than the hard silica coating. Although all NOM fractions weakly interacted with TA even at high Na+ concentrations, these organics adsorbed on the silica-coated AgNPs; thus, inducing stability. Humic fractions provided higher colloidal stability due to stronger electrostatic/steric interactions. Ca2+ increased the aggregation kinetics of both capped nanoparticles in the absence and presence of NOM. However, the aggregation kinetics of TA-coated AgNPs in humic NOM-containing solution were higher than those of non-humic due to a higher content of deprotonated carboxyl groups and cation bridging mechanisms. The knowledge compiled in this study would assist in understanding and pbkp_redicting the fate and transport of capped nanoparticles in natural aquatic systems of different compositions.